The present invention relates to improvements in hinges in general, and more particularly to improvements in hinge joints of the type wherein two substantially plate-like components or leaves are coupled to each other for angular movement relative to one another. Such hinge joints can be used for a variety of purposes, for example, to allow for adjustment of the back of a seat relative to the remainder of the seat in a motor vehicle or the like. Still more particularly, the invention relates to improvements in hinge joints of the type wherein the leaves are provided with integral means for holding them in selected angular positions relative to one another in such a way that the angular position of one leaf relative to the other leaf and/or vice versa is changed only when desired by the operator. Such holding means constitute or comprise at least one spur gear with an annulus of active teeth and at least one internal gear or ring gear with an annulus of active internal teeth whereby the spur gear extends into (i.e., it is surrounded by) the internal gear and is in mesh with the latter.
It is already known to convert sheet metal blanks into components of hinge joints with meshing internal and spur gears by resorting to a punching or stamping operation so that each active tooth (namely the tooth which transmits or receives motion) is disposed at one side of the finished stamping and the other side of the stamping is formed with passive teeth which alternate with the active teeth and do not serve to transmit motion but are formed by the die simply as a result of resort to a stamping or punching technique. Such stampings are formed in precision stamping or punching machines. It is important to ensure that all active teeth of the spur gear and of the internal gear assume an optimum shape and size to allow for adequate transmission of motion as well as for proper retention in a selected angular position. Due to the nature of the technique which is resorted to in connection with the making of such stamped components, the outlines of active teeth are not sharp, especially in the regions of their top lands. As a rule, the top lands are slightly rounded due to shrinkage in the course of the stamping operation so that the effective width of active teeth, as considered in the axial direction of the respective gear, is reduced due to the fact that the gears are made from blanks in a stamping or punching press. Consequently, shrinkage or shifting of the material of blanks in the regions of top lands or tips of the active teeth must be taken into consideration in selecting the thickness of blanks in order to ensure that the gears of the finished components will be capable of transmitting forces which are likely to develop in actual use of the hinge joint. In other words, the thickness of blanks which are converted into the components of the aforediscussed hinge joint is actually excessive, and this is attributable to the fact that the stamping or punching operation involves a flow of the material of blanks in directions to reduce the effective width of certain portions of the thus obtained active teeth.
The aforementioned copending patent application Ser. No. 376,846, now U.S. Pat. No. 4,469,376, discloses a hinge joint wherein the blanks undergo a certain treatment which is designed to shift some material toward the top lands of active teeth. This is accomplished by the provision of so-called punching indentations which are impressed into selected portions of the blanks to cause some material to flow toward the unsatisfactory portions of active teeth which are formed in a stamping press. To this end, the components are formed with circumferentially complete grooves in the regions of dedendum circles of teeth of the spur gear as well as the internal gear. This causes some material flow toward the top lands and imparts to the tips of teeth a more or less polygonal shape of a more satisfactory width, as considered in the axial direction. However, the provision of such grooves entails a weakening of active teeth in the region of their root portions, i.e., the thickness of junctions between the roots of active teeth and the remaining portions of each of the two gears is reduced by the depth of the respective grooves.